Speech and speech processing

• "Verfahren zur Erzeugung von Klaengen fuer elektronische Musik", Ludwig Heck & Fred Buerck, German Patent DE1051100, 1959.
• "Verfahren zur Erzeugung von Klaengen fuer elektronische Musik", Ludwig Heck & Fred Buerck, German Patent DE1080386, 1960. The first patents illustrating the use of single-sideband modulation as an electronic music technique, known as a Klangumwandler, or Frequency Shifter.

Concerning nondigital devices for independently altering the duration and pitch of recorded signals, called by many names, including: Information Rate Changers, Time Stretcher/Compressors, Zeitdehner, and Pitch-and-Frequency changers.

• "Method of and Apparatus for Varying the Length of Sound Records", Berthold Freund, US Patent 1996958, 1935. method of varying relative read and write speeds of optical recordings.
• "Sound Translating Apparatus", E Schueller US Patent 2195192, 1940. a non-rotating head
• "Sound Reproducer", E Schueller US Patent 2352023,1944. rotating head with multiple "overlapping" reproducers to stretch or compress time scale without altering pitch.
• "Recording Device", Fairbanks, Everitt, & Jaeger, US Patent US2886650, 1959.
• "Recording Device", Fairbanks, Everitt, & Jaeger, Canadian Patent ÊCA639831, 1962.
• "Method and Device for Producing Signals or Sound", Fairbanks, Everitt, & Jaeger, Canadian Patent CA639832, 1962.
• "Recording and Method of Making Same", Fairbanks, Everitt, & Jaeger, Canadian Patent CA640070, 1962.

From Anton Springer came the Springer Machine used in many european tape studios.

• "Rotatable electromagnetic transducers", Anton Springer, US PatentÊUS2977423, 1961.
• "Rotatable electromagnetic transducer system", Anton Springer, US Patent US3022383, 1962.
• "Rotatable magnetic systems for transforming audio currents", Anton Springer, US Patent US3047673, 1962.
• "Electromagnetic transducer", Anton Springer, US Patent US3064088, 1962.
• "Magnetic recording and playback systems", Anton Springer, US PatentÊUS3077587, 1963.

Concerning artificial reverberation

• "Electric Musical Instrument Reverberation Nonlinear Control System", H Laube, US Patent 3463868. 1969
• "Sound Signal Delay Device", N Tsuchiya, US Patent 3721925. 1973. uses acoustic tubes.